View Single Post
Old 12th Oct 2018, 2:33 pm   #17
PsychMan
Octode
 
PsychMan's Avatar
 
Join Date: Jun 2013
Location: Fleet, Hampshire, UK
Posts: 1,764
Default Re: Miniature relay Suppressor

Quote:
Originally Posted by Wendymott View Post
In the 80's our company was requested to look at the problem of Beer Cooler compressor motors killing the relay switch module. The Peak voltage was horrendous as the contacts opened, killing the relay drive transistor, thus keeping the relay on, thus the Ice bank becoming solid ice.
We had little room to fit an R/C snubber circuit, thus we bought many 1000 VDR's (voltage dependant resistors)... I cannot remember the value at which they conducted, but Farnells were well happy. We drilled two holes one either side of the relay/ motor contacts.
As I say we retro fitted many 1000, NO returns... Eventually IMI paxman who made the coolers, had them fitted at source.
The hardest part of the whole operation was removing the pcb that was mounted in a tight fitting plastic case, a lot of sealant was used in some versions, and none in others..
I seem to remember the VDR's were rated at 300/400V.... but as I say.. its a long time ago.
So they were installed across the relay contacts. I assume these are metal oxide varistors (MOVs)? I wonder what kind of service life such a component would have as they apparently break down gradually with use. Your comment suggests they last very well indeed with repeated cycling of the compressors.

I used one in a similar application (but across the load) for a fridge compressor with a solid state relay. I was concerned about longevity though so removed it. Touch wood, the solid state relay has held up just fine. Though it has an integral snubber and is rated for industrial use (50 amps), its also zero crossing. Been running for months in this configuration and no problems yet

Last edited by PsychMan; 12th Oct 2018 at 2:59 pm.
PsychMan is offline